Process of using sodium silicate to create fire retardant products

ABSTRACT

Wood products, specifically wood commonly used in construction including dimension lumber, pressure treated pine, composite wood materials such as plywood, particle board, and wafer board, and samples of paper and fabric were variously treated with concentrations of sodium silicate (Na 2 O.SiO 2 ) also known as water glass. Cellulosic materials including dimension lumber, plywood, particle board, wafer board, paper, and fabric were treated with sodium silicate (Na2O.SiO2) in concentrations ranging from 400-0.04 g Na2O.SiO2/kg water. To overcome the disadvantages of sodium silicate, sodium silicate treated samples were further treated to convert the water soluble sodium silicate to a water insoluble form, thereby overcoming the disadvantages of water solubility and rendering the material effective for internal and external uses. Although treated sodium silicate samples are composed of the same elements in similar proportions, as the untreated sodium silicate samples, the water solubility of the treated and untreated substances is very different.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional application is a continuation of U.S. applicationSer. No. 10/870,985, filed on Jun. 21, 2004, now U.S. Pat. No.7,297,411; which was a continuation of U.S. application Ser. No.09/927,062, filed on Aug. 10, 2001, now U.S. Pat. No. 6,827,984; whichwas a division of application Ser. No. 08/818,195, filed Mar. 14, 1997,now U.S. Pat. No. 6,303,234, which in turn was a non-provisionalapplication claiming the benefit of provisional application Ser. No.60/013,452 (filed Mar. 15, 1996, in the names of Karen M. Slimak andRobert A. Slimak, entitled “Using Sodium Silicate to Create FireRetardant Products”) and provisional application Ser. No. 60/040,709(filed Mar. 14, 1997 in the names of Karen M. Slimak and Robert A.Slimak, entitled “Effectiveness of Sodium Silicate and Micro-layers ofSilicon Oxide Glassy Films in Imparting Fire Retardant Properties andMoisture Resistance to Cellulosic Materials”) the entire disclosures ofwhich are being incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The purpose of this invention is to provide 1) sodium silicate (waterglass) impregnated wood materials introducing a fire retardant propertyto wood products, 2) water glass impregnation of other materials, suchas paper and cloth, in such a way as to allow their intended functionswhile reducing the risk of flammability, and 3) wood products treatedwith sodium silicate can be used simultaneously to impart flameresistant properties to wood and to cause the wood to become termiteresistant, providing an environmentally friendly method for long termtermite control.

Liquid sodium silicate (water glass), applied to the surface of variousproducts, can impart fire retardant properties. In the presence of fire,the sodium silicate will form foam-like crystals that help to provide aninsulating barrier between the product and the flame, and will thus slowdown the spread of fire. Wood and other products will become lessflammable when treated with sodium silicate. The foam-like productappears to be more than a mere change in form of the sodium silicate. Itis believed that the foam-like material is the product of a chemicalreaction, and also imparts fire retardant properties to the materialtreated with sodium substrate.

It is a further purpose of the invention to provide a polymerized formof sodium silicate that is water insoluble: As a result of theapplication of heat, the sodium silicate undergoes dehydration (loss ofwater) and a process of polymerization that forms increasingly largermoieties of (SiO₄)_(n) ⁻¹ while still maintaining an overall charge of−1 that forms an association with the free sodium. As the materialpolymerizes the resultant material increases in size to the point thatit is no longer able to dissolve in water, thus becoming insoluble.

Cellulosic materials including dimension lumber, plywood, particleboard, wafer board, paper, and fabric were treated with sodium silicate(Na₂O.SiO₂) in concentrations ranging from 400-0.04 g Na₂O.SiO₂/kg waterand the surfaces of selected samples were further treated with siliconmonoxide (SiO), applied in a molecular layer by vapor deposition. Testswere conducted to determine the effectiveness of these materials interms of fire resistance, durability, duration of effectiveness, andmoisture resistance.

Sodium silicate treated samples were further treated by the depositionof a molecular coating of silicon monoxide by vapor deposition. Samplestreated by this technique were found to be completely moistureresistant. The combined application of sodium silicate and siliconmonoxide was found to provide a fire retardant product that is moistureresistant and decomposition resistant, and therefore effective forinternal and external uses. Sodium silicate coated with a thin layer ofsilicon monoxide does appear to provide an effective fire retardantmaterial.

The purpose of this invention is also to provide 1) sodium silicate(water glass) impregnated wood materials will introduce a fire retardantproperty to wood, paper and cloth products, 2) the chemical and physicalalternations of wood and other samples impregnated with sodium silicate,3) the effects of moisture, air, temperature fluctuations, andweathering on sodium silicate treated samples, and 4) silicon oxideapplied as a micro-layer to the surface of sodium silicate treatedmaterials as an effective moisture barrier and guard against long termdeterioration.

Liquid sodium silicate (water glass), applied to various products, canimpart fire retardant properties. In the presence of fire, the sodiumsilicate will form foam-like crystals that help to provide an insulatingbarrier between the product and the flame, and will thus slow down thespread of fire.

In addition the sodium silicate penetrates the interiors of porousmaterials altering cellular structures and forming many microscopicallythin glassy layers. A micro-layer of silicon oxide applied to thesurface of a sodium silicate-treated material will make the materialwaterproof as well as prevent long term deterioration.

This invention provides impressive fire retardant properties for sodiumsilicate treated samples that would make this material all that would bedesired in a fire retardant—highly effective, water insoluble, providingstrengthening properties, and economical.

A further purpose of this study is to apply sodium silicate solutions tovarious samples for the purpose of evaluating the fire retardantproperties of the resultant products. In the presence of fire, it isanticipated that the presence of non-combustible sodium silicate willrender the cellulosic material less available to the flame and willretard vaporization of the cellulosic material; also sodium silicate isexpected to form foam-like crystals that help to provide an insulatingbarrier between the product and the flame which will further separatethe sample and the fire source, helping to reduce the temperature of thesample thus slowing down the spread of fire.

Sodium silicate is defined as water soluble (Condensed ChemicalDictionary, 1971). However, during pilot studies, it was noticed that assodium silicate is exposed to large amounts of heat, parts of sodiumsilicate buildup would foam up, and this foam was water insoluble. Thisraised questions about the effect that excessive heating was having onsodium silicate. It was also noticed that when sodium silicate treatedwood was subjected to heat from a flame torch, the flame was anorange/yellow color, as opposed to the light yellow traditional color ofuntreated wood burning. Two kinds of experiments were devised to examinethe changes in sodium silicate that occur during exposure to intenseflame and heat in the presence of wood. The first test was to examinewater solubility versus temperature. The solubility of sodium silicatewas measured after being exposed to different temperatures. The secondtest utilized an x-ray photoelectron spectrometer to examine thechemical composition of foamed sodium silicate byproducts.

Sodium silicate was expected to penetrate the interior of porousmaterials, altering cellular structures and forming many microscopicallythin glassy layers. It is anticipated that the presence of sodiumsilicate was evident microscopically, and that the distribution patternsand interaction with cellular structures were discernible.

Products treated with sodium silicate were tested for durability,strength, and ability to withstand the effects of prolonged exposure toair, moisture, and weathering.

2. Description of the Related Art

Throughout history, house fires have been a major threat to thewell-being of many families. According to the National fire ProtectionAssociation, in the United States in 1995 there were 600,000 structuralfires in homes and businesses, causing approximately $7,620,000,000 indamages to property. The average loss per fire was $12,700. Over 30,000people were injured in fires; there were 4585 deaths (12-13 per day) dueto fire.

The possibility of awakening to the spectre of threatening flamesstrikes fear in the hearts of many, including this author, who wasawakened to the acrid smell of smoke early on the morning of Jan. 26,1995. An electrical fire in the garage had spread to nearby materialsand had become a raging inferno before being discovered by a familymember. The damage in this fire approached $150,000, but fortunately theeffects on health were limited to a minor case of smoke inhalation.Unmeasured is the lingering fear, the memories of billowing smoke andfire, and the uneasy knowledge that it could and just might happenagain, and that next time the damages might not be limited to property.

In spite of years of research, the United States remains the leaderamong developed nations in the number of fires occurring per year, thenumber of injuries and lives lost to fire, and total dollar value ofproperty losses due to fire. The injuries and losses of life due to fireare highest among the elderly (more than double the average population),the infirm and among children. In spite of efforts to the contrary, themonetary damages, numbers of injuries and loss of life are likely toincrease substantially in the future.

Fires occur in homes and business largely because of the flammability ofthe materials of construction and the large quantities of flammablematerials placed in homes, offices and other buildings. Fires frequentlystart with a small flame or a spark that may last only a few seconds.The flames grow because this quick release of energy ignites nearbymaterials that are readily flammable especially when there is an amplesupply of air. The flames then spread to other materials and grow insize and heat intensity. As the temperature increases the kindlingtemperature of other less flammable materials is reached and they canignite suddenly causing the fire to spread quickly.

In recent years due to increasing costs for wood, there have been majorschanges in the type of wood used in home construction. Historically,solid wood products were used as primary building materials in homes,for example 2×4's and 1×4's were used for framing, and rough wood plankswere used for sub flooring and roofing support structures. The trendover the past several years has been to convert more and more from solidmaterials to composite materials. This is due to decreased costs forcomposite materials, and to the fact that many composite materials haveadvantages of lighter weight, less warping and increased strength. Inthe rush to convert to composite materials, properties related toflammability may not have received due consideration.

FIG. 1 compares weight loss profiles of 2×4 dimension lumber, 1×4dimension lumber, 1×4 pressure treated pine, roofing shingles, plywood,pressed wood and wafer board samples. All samples were 30 cm in length,and were tested in a chamber in which two propane torches were appliedto the bottom surface of each sample according to the proceduresdescribed elsewhere in this paper.

The data show that 2×4 samples exhibited the slowest rates of burn andthe lowest weight loss of all samples tested. Although 2×4 lumber [10]definitely will burn, the combined effects of two torches appliedindefinitely was insufficient to cause a 30 cm sample to ignite and burnspontaneously. All other samples [11-16] ignited and burned readily;however, 1×4 pressure treated pine [11] and 1×4 untreated dimensionlumber [12] generally showed slower times for ignition and lowercombustion rates that the remaining samples [13-16] as follows: [13]particle board, [14] plywood, [15] shingle, and [16] wafer board.

Data listing ignition times and combustion rates is presented in Table 1and in FIG. 2. The data for wafer board, shingles and plywood wasparticularly important because the steep slope of the weight lossprofiles for these samples indicated that between 20 and 70 percent ofthese samples were burned per minute. Plywood (70%/min) is the materialof choice in most homes for subflooring, subroofing and occasionally inwalls of homes. Wafer board is becoming increasingly popular as astructural material, replacing 2×4's and 4×4's. Each of these threematerials was completely consumed in 2-6 minutes in the standard firetests conducted. In FIG. 2 [17] represents the results of combustionduration (min) for 2×4 lumber; the test was stopped at 60 minutes, inthe sample only, combustion was incomplete. In FIG. 2 [18] indicatesthat spontaneous burning did not occur in the 2×4 lumber sample.

TABLE 1 Burn Characteristics of Common Building Materials Ignition TimeCombustion rate % of Sample Combustion Building Material (min) (%sample/min) Consumed Completed (min) 2 × 4 dimension lumber >60 1.6 3320 (test ended) 1 × 4 pressure treated pine 5 6.7 89 18 1 × 4 dimensionlumber 1 6.5 87 15.5 particle board 1.2 7.1 79 10.5 wafer board 3 23.388 6 shingle 0.17 21.1 80 4 plywood 0.2 70.7 85 2.5

Currently, new homes are frequently constructed with sub floors, subroofs, and all structural components incorporating plywood and waferboard, highly flammable materials that burn at a rate 13 to 45 timesgreater than that of 2×4 dimension lumber.

There is therefore a need to identify building materials that providethe desired construction-properties and yet decrease the flammability ofthe materials to below that of 2×4 dimension lumber. There is also aneed to increase the fire retardant properties of furniture, fabrics,paper and other combustible materials that are stored inside structures.

Materials to be made resistant to fire in the present study—wood, woodcomposites, paper and fabric—are primarily natural polymers. As has beendemonstrated above, these substances vary in flammability due to thenature of the polymers, and the density and particle size of thesubstance, e.g. 2×4 very dense with large particle sizes, and looselywoven fabric—low density with small particle sizes.

The major problems preventing widespread use of fire retardants are thecosts of use, effects on physical properties of the treated materials,the water solubility of most fire retardant chemicals, making thetreated samples vulnerable to leaching, and the lack of regulationsrequiring the use of these materials.

Based on the fact that the burn characteristics described above (FIG. 1)were obtained from samples purchased randomly in retail outlets, thisinvestigator concluded that the fire retardants described in theliterature have not yet developed attributes that are sufficientlyattractive to be implemented in large scale in commercial applicationsin wood products. Therefore this investigator decided to search foranother substance to use in fire retardant applications.

This investigator observed that sodium silicate exhibited strongadhesive properties in addition to being a noncombustible material, andtheorized that the adhesive properties might be used to provide fireretardant properties in certain products. This investigator wasintrigued by the fact that the possible incorporation of glass-likematerials into wood and other products potentially would possiblystrengthen the products as well as impart fire retardant properties.

This investigator coated small samples of wood and noticed that when thesodium silicate treated samples were applied to a flame, sodium silicateresidues formed bubbles that provided a physical barrier against theflame in addition to reducing available access to flammable materials byoxygen, as heating continued the sample became incandescent. It appearedthat as sodium silicate formed bubbles and droplets, the wood remainedunaffected by the flame.

The idea for this invention came to me easily. My sister was using waterglass to glue glass planes together to make test chambers for herscience fair project. I wondered if it was possible to coat wood withwater glass and help make the wood fire retardant. As I watched her workwith the water glass, I played around with it and coated small pieces ofwood and noticed that when the pieces were applied to a very hot flame,the water glass bubbled over forming a natural barrier against theflame. Thus, it appeared to me that as the sodium silicate formedbubbles, the wood remained unaffected by the flame.

A fire retardant material is one having properties that providecomparatively low flammability or flame spread properties (ASTM 1992).There are a number of materials that have been used to treat wood forfire retardancy including ammonium phosphate, ammonium sulfate, zincchloride, dicyandiamide-phosphoric acid and sodium borate. Solutions ofthese fire-retardant formulations are effective when injected into thewood under pressure (Condensed Chemical Dictionary 1971). The sodiumsalts of silicon, or water glass, however, have not been identified as afire retardant. If my hypothesis is correct, that water glass is aneffective fire retardant when applied as a coating, then it could be animportant finding since it is virtually non-toxic, safe to use,relatively cheap, readily available and can be easily used by thehomeowner.

Sodium silicate (water glass) is a member of the family of solublesodium silicates and is considered the simplest form of glass. Theformula varies from Na₂O₃SiO, to 2Na₂OSiO₂ depending on the proportionsof water. The composition used in this study was a 40 percentconcentration. Water glass is derived by fusing sand and soda ash; it isnoncombustible with low toxicity. It is used as catalysts and silicagels; soaps and detergents; adhesives; water treatment; bleaching andsizing of textiles and paper pulp; ore treatment; soil solidification;glass foam; pigments; drilling muds; binder for foundry cores and molds;waterproofing mortars and cements; and impregnating wood. The latteruse, however, has not been linked with fire retardancy (CondensedChemical Dictionary 1971).

The terms used with flame-resistant materials are sometimes confusing.Fire resistance and flame resistance are often used in the same contextas the terms fireproof or flameproof. A material that is flame resistantor fire resistant does not continue to burn or glow once the source offire has been removed, although there is some change in the physical andchemical characteristics of the material. Fireproof or flameproof referto material that is totally resistant to fire or flame, such asasbestos. Most organic material like wood undergo a glowing action afterthe flame has been eliminated. This “afterglow” may cause as much damageas the flaming itself.

The mechanisms of fire-retardancy are complicated. The coating theoryreveals that fire resistance is due to the formation of a layer offusible material which melts and forms a coating, thereby excluding theair necessary for the flame to propagate. This theory, first reported byGay-Lussac in 1821, was the basis for the development of fusible saltssuch as carbonates, borates, and ammonium salts. The gas theorytheorizes that the flame retardant produces noncombustible gases whichdilutes the flammable gases. The thermal theory suggests that the flameis dissipated by an endothermic change in the retardant and the heatsupplied from the source is conducted away from the wood so fast thatcombustion temperatures are never reached. Chemical theory says that thestrong acids and bases (water glass is a strong base) impart some degreeof fire retardancy (Concise Encyclopedia of Chemical Technology 1985).

My theory, and the basis for my hypothesis, is that sodium silicate canmake wood and other products fire retardant. The sodium silicate willenter the voids in the wood, and harden into glass. The sodium silicatewill separate the wood fibers from one another, and not allow burning.Any flame applied to the samples will not burn or spread, because itcomes in direct contact with the sodium silicate. The preliminaryobservations I made on my own with sodium silicate and small pieces ofwood showed that when in contact with a very hot flame, the sodiumsilicate bubbles over, forming a natural barrier against the flame andthe wood remains unaffected by the flame.

To test my theory, I decided to treat (by dipping and soaking) dimensionlumber with different concentrations of water glass and to burn thetreated products with a propane torch to determine the potential forfire retardancy.

SUMMARY OF THE INVENTION

Dimension lumber (1″×4″×12″ pine and 2″×4″×12″ spruce), 1″×4″×12″pressure treated pine samples and composite materials were treated withsodium silicate by dipping (a 24-hour exposure) and soaking (a 7-dayexposure) in water glass. Paper and cloth samples were similarlytreated. The samples were then air dried at room temperature for aminimum of seven days. To test for fire retardancy, the wood sampleswere subjected to a hot flame from two propane torches for 20 minutes,and the paper and cloth samples were subjected to a candle flame. Dataon flame propagation, afterglow, ash development and weight loss werecollected during and after the burns. To measure variability, fourreplicates of each sample were burned along with an untreated sample (acontrol), and a sample treated with sodium borate, a known fireretardant chemical.

Samples were examined microscopically to determine characteristics ofthe distribution of sodium silicate within the samples. Sodiumsilicate-treated samples of 1×4 pine, shingles, wafer board and largepopsicle sticks were treated with ultra-thin layers of silicon oxide.Sodium silicate treated samples were also oven cured and were subjectedto flame to convert them to glass thus imparting strength, further fireretardant properties and added strength. The samples were tested forfire retardant properties by the usual methods, for moisture resistanceby exposure to boiling water and examining microscopically for evidenceof sodium silicate crystals, and for strength by compression tests.

A possible solution to both the problem of moisture-related leaching anddeterioration during air exposure was identified.

It was hypothesized that after being treated with sodium silicate, if alayer of silicon oxide were deposited over all surfaces, the resultingproduct will retain its flame retardant properties as well as becompletely water proof and completely resistant to deterioration due toexposure to air or the effects of weathering. Because extraordinarilysmall amounts of silicon oxide would be used, the added costs would beexpected to be small.

The present invention thus involves a process of imparting fireretardant properties to a cellulosic material comprising coating acellulosic material with sodium silicate by contacting a sodium silicatesolution with the material to be coated, dehydrating the coating, anddepositing a coating of a silicon oxide glassy film on the sodiumsilicate coated material. In one embodiment, the coating of siliconoxide is a monomolecular layer of silicon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the weight loss profiles for each of the following buildingmaterials: a) 2×4 lumber, b) 1×4 pressure treated pine, c) 1×4 lumber,d) particle board, e) wafer board, f) shingle, and g) plywood.

FIG. 2 compares combustion parameters

FIG. 3 shows weight loss of samples in flame tests with 1×4 dimensionlumber.

FIG. 4 compares weight percent water glass and weight percent burn lossin 1×4 dimension lumber.

FIG. 5 shows weight loss all samples, 1×4 pine treated with water glass.

FIG. 6 shows weight loss of samples in flame tests with 1×4 pressuretreated lumber.

FIG. 7 shows weight loss for all samples, 1×4 pressure treated pinetreated with water glass.

FIG. 8 shows fire retardant effect of water glass on plywood.

FIG. 9 shows fire retardant effect of water glass on particleboard.

FIG. 10 shows fire retardant effect of water glass on wafer board.

FIG. 11 shows fire retardant effect of water glass on cloth strips.

FIG. 12 shows fire retardant effect of water glass on slurried clothstrips.

FIG. 13 compares weight percent water glass and fire retardant effect incloth.

FIG. 14 shows fire retardant effect of water glass on paper.

FIG. 15 shows fire retardant effect of water glass on slurried paper.

FIG. 16 compares weight percent water glass and fire retardant effect inpaper.

FIG. 17 shows paper slurry with water glass: percent weight loss overtime.

FIG. 18 shows paper slurry with water glass: percent weight loss overtime.

FIG. 19 compares water glass results to controls.

FIG. 20 compares boric acid results to untreated control.

FIG. 21 shows the relationship between increasing flammability incontrol samples and increasing effectiveness in water glass treatedsamples.

FIG. 22. shows a cross section of yellow pine sample soaked in 300 g/k,aqueous sodium silicate, and shows sodium silicate spreading inwardthrough cellular structures.

FIG. 23 shows results of X-ray crystallography examination of sodiumsilicate fragment modified by heat at 620° C., showing non crystallinestructure present.

FIG. 24 shows results of examination by x-ray photoelectron spectrometryof sodium silicate fragment modified by heat at 620° C., showing theelemental composition.

FIG. 25 shows the effect of temperature on solubility of sodiumsilicate.

FIG. 26 shows the weight loss profile of sodium silicate/siliconmonoxide treated samples

FIG. 27 shows the weight loss profile of sodium silicate treatedcontrols

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Wood products, specifically wood commonly used in construction including1″×4″×12″ pine, 2″×4″×12″ spruce, 1″×4″×12″ pressure treated pine,composite wood materials such as plywood, particle board, and waferboard, and samples of paper and fabric were treated with differentconcentrations of sodium silicate (Na₂O.SiO₂) also known as water glassto test the hypothesis that water glass would make these products fireretardant. Using a propane torch as a fire source, the results show thatfire retardancy was greatest at the highest concentrations of waterglass and all water glass treated samples were more fire retardant thanthe untreated controls. In general, the more easily combustible thesubstance studied, the greater was the fire retardant effect of sodiumsilicate. Upon application of the torch, the sodium silicate bubbled upand became crusty; thus providing a physical barrier against flamespread. The treated samples would only burn in the most intense part ofthe flame, with virtually no flame propagation. All of the untreatedcomposite samples and pressure treated samples burned particularlyvigorously, and thoroughly. The most easily burned wood-based untreatedcontrol was wafer board which proved to be highly combustible. Of allwood-based samples wafer board flame resistance was the most improvedafter treatment with water glass. The greatest difference between thetreated samples and the control was found with samples that were highlyflammable for example paper and cloth. In addition, since most firesstart with flammable materials inside a building such as with paper anddrapery, the findings that flammability can be reduced by up to 90% withthe use of water glass, suggests that this substance may have potentialfor fire prevention in paper and cloth products. Water glass is readilyavailable, is relatively cheap and virtually non-toxic It can be appliedto wood at industrial wood-preserving operations and can be easilyapplied by the homeowner. Sodium silicate, water glass, does appear tobe an effective fire retardant chemical.

Treating the Samples with Water Glass

Dimension Lumber: Pieces of kiln-dried 1″×4″ pine dimension lumber,2″×4″ spruce dimension lumber, and pieces of 1″×4″ pressure treatedlumber were placed in plastic tanks (dimensions 2 ft×1 ft×8 in) filledwith water glass solutions to a depth of 6″. The pieces were placed inthe tank in such a way that they were completely submerged and yet notin direct contact with each other. For the “Soak-Treated” lumber, thepieces remained in the treatment tanks for seven days after which timethe pieces were removed from the tank and placed for seven days on adrying apparatus designed to keep the wood pieces from touching all butvery small occasional supporting points. The borax treated sample wasprepared similarly using a saturated aqueous solution consisting ofseven (7) parts of sodium borate (Borax®) and three (3) parts boricacid, by weight. The controls were not treated. The wood was weighedbefore and after treatment with the fire retardants. The same procedureswere used for the “Dip-Treated” wood except the wood was submerged inthe solutions of fire retardants for only 24 hours.

Composite Materials: Pieces of wafer board, plywood and particle boardwere made and then treated with water glass. For the wafer board and theparticle board, sawdust or wood shavings were mixed with 100% waterglass until the mixture was damp, thoroughly wet, and compressible. Thenportions of the mixture were compressed in a form under pressure forapproximately 24 hours. The water glass-wood composite materials wereremoved from the forms and allowed to dry for seven days. The plywoodwas made from balsa wood which was soaked for seven days in 100% waterglass. Then the pieces were assembled in 5 layers with alternating grainpatterns to form a final plywood sample 3″×9″×½″. The plywood was driedunder pressure using clamps for seven days to achieve the desired shapeand density. The borax treated samples were prepared similarly using asaturated aqueous solution consisting of seven (7) parts of sodiumborate (Borax®) and three (3) parts boric acid, by weight. The remainingcontrols were not treated. The wood was weighed before and aftertreatment with the fire retardants.

Eight samples each of wafer board, plywood and particle board were madeand treated with water glass. Sodium silicate was used as the fireretardant and as the adhesive material forming the composite. For waferboard and particle board samples, sawdust or wood shavings were mixedwith 400 g/kg water glass until the mixture was damp, thoroughly wet,and compressible. Then portions of the mixture were compressed in ateflon-lined form for approximately 24 hours. The water glass-woodcomposite materials were removed from the forms and allowed to dry forseven days. Plywood was made from balsa wood which was soaked for sevendays in 400 g/kg water glass. The pieces were then assembled in 5 layerswith alternating grain patterns to form plywood samples with dimensions3″×9″×½″. The plywood was dried under pressure using clamps for sevendays to achieve the desired shape and density. Borax treated sampleswere prepared by soaking commercially manufactured pieces of plywood forseven days, in the manner described above for 1×4 lumber, using asaturated aqueous solution consisting of seven (7) parts of sodium,borate (Borax®) and three (3) parts boric acid, by weight. Untreatedsamples of wafer board, plywood and particle board were used ascontrols.

The above described procedures for preparation of composite materialswith 400 g/kg sodium silicate were repeated using a 40 g/kg solution ofsodium silicate, and then repeated again using a 4 g/kg solution ofsodium silicate.

Cloth samples: Eight pieces of water glass-impregnated cloth test pieceswere each made by combining 50 g water glass and water, 200 g water andlaundry lint. The mixture was spread thinly on a screen and dried forseven days. The product was a felt-like material 4 in×12 in. For thecontrol cloth test pieces were made as described above without theinclusion of water glass. Two additional test samples were prepared bycombining laundry lint and water and adding a saturated aqueous solutionconsisting of seven (7) parts sodium borate (Borax®) and three (3) partsboric acid, by weight, in amounts suitable to form a finished clothproduct, and then drying. Another untreated control was also used.

In addition, to better understand and examine the use of sodium silicatefor cloth and fiber applications, eight pieces of cotton knit fabric, 6in×2 in, were immersed in each of the following concentrations of sodiumsilicate: 40 g/kg, 4 g/kg and 0.4 g/kg. The procedure for sodiumsilicate treatment of all knit fabric samples were identical, except forthe variation in sodium silicate concentration, and was as follows:Eight swatches of fabric, 6 in×2 in, were placed in a large beaker andsubmerged in a 1 liter solution containing one of the above listedconcentrations of sodium silicate. The container was tightly covered andthe solution was gently stirred for 48 hours by means of a teflonstirring bar magnet. The samples were then removed and dried on a metalmesh screen for eight hours followed by final drying on teflon sheetsfor one day. Control samples were prepared by similarly immersing 8each, cotton knit samples into distilled water for 48 hours and thendrying as for the treated samples. Control samples, 8 each, of asaturated aqueous solution of sodium borate and boric acid were alsoprepared in the manner described above for sodium silicate treatedsamples. Fiber samples were microscopically examined to ascertain thedistribution of sodium silicate among the cotton fibers, and were testedfor flammability as described below.

In addition, samples of treated surgical cotton were prepared in orderto study the nature of sodium silicate penetration into natural fibersand to determine the potential for use of sodium silicate as anupholstery stuffing. Eight samples each of 400 g/kg, 40 g/kg, 4 g/kg,0.4 g/kg, and 0.04 g/kg sodium silicate treated gauze were prepared asfollows: 8 each, 25 g samples of surgical cotton were immersed in abeaker containing a 1 liter solution of sodium silicate, for example a40 g/kg solution. The container was tightly covered and the solutionwere gently stirred for 48 hours by means of a teflon stirring barmagnet. The samples were then removed and dried on a mesh screen foreight hours followed by final drying on teflon sheets for one day.Control samples were prepared by similarly immersing 8 each, 25 g piecesof cotton batting into distilled water for 48 hours and then drying asfor the treated samples. Control samples, 8 each, of a saturated aqueoussolution of sodium borate and boric acid were also prepared in themanner described above for sodium silicate treated samples.

Paper samples: Eight pieces of water glass-impregnated paper test pieceswere each made by combining 50 g water glass and water and 200 g waterand 6 sheets of pulverized paper. The mixture was spread thinly on ascreen and dried for seven days. The product was a coarse paper material4 in×12 in. The untreated control was made without water glass. Twoadditional test samples were also prepared by combining pulverized paperand water and adding a saturated aqueous solution consisting of seven(7) parts sodium borate (Borax®) and three (3) parts boric acid, byweight, in amounts suitable to form a finished paper product containingborax, and then drying.

Sodium silicate impregnation of paper was also accomplished by immersing6 in×2 in sheets of paper in sodium silicate solutions. Eight pieces ofpaper, 6 in×2 in, were immersed in each of the following concentrationsof sodium silicate: 40 g/kg, 4 g/kg, 0.4 g/kg and 0.04 g/kg. Theprocedure for sodium silicate treatment of all paper samples wasidentical, except for the variation in sodium silicate concentration,and was as follows: Eight swatches of paper, 6 in×2 in, were placed in alarge beaker and submerged in a 1 liter solution containing one of theabove listed concentrations of sodium silicate. The container wastightly covered and the solution was very slowly and gently stirred for48 hours by means of a teflon stirring bar magnet. The samples were thenremoved and dried on a mesh screen for eight hours followed by finaldrying by ironing on a teflon ironing board cover. Control samples wereprepared by similarly immersing 8 each, paper samples into distilledwater for 48 hours and then drying as for the treated samples. Controlsamples, 8 each, of a saturated aqueous solution of sodium borate andboric acid will also be prepared in the manner described above forsodium silicate treated samples. Fiber samples were microscopicallyexamined to ascertain the distribution of sodium silicate among thecotton fibers, and were tested for flammability as is described below.

High pressure apparatus: Samples (6 in×4 in×1 in pine) were placed in ahigh pressure chamber of original design. The chamber was filled with400 g/kg sodium silicate and hand pumped to a pressure of 1000 psi. Eachsample was maintained at this pressure for 30 minutes. After which timethe pressure was released and the sample was allowed to dry. Each samplewas then subjected to the propane flame tests described below.

Termite Reaction to Water Glass Treated Samples

Thirty small pieces of wood, 0.5 in on a side, were treated with waterglass as described above for 100% water glass with a seven day soakingperiod and subsequent seven day drying period. Other pieces of wood, ofidentical size, that are not water glass treated were used as controls.Thirty pieces of water glass treated wood cubes were placed in each of a1-quart glass test chamber. A second test chamber contained onlyuntreated wood cubes. Worker termites and moist paper towels were addedto each container to form a suitable terrarium environment. Termiteactivity was be observed for 2 months.

Burn Testing

High-Temperature Propane Burn Tests: Both the treated and untreated woodwas subjected to a 2500° F. flame supplied by a “Bernz-O-Matic” 400 gmpropane fuel cylinder with a JT-680 tip (Model TX-9). The wood wassuspended vertically, side-by-side, approximately 10 inches apart from ametal rack made from copper tubing and designed to burn six (6) piecesof wood simultaneously. Each “burn” event consisted of burning sixpieces of wood: four (4) treated pieces; one (1) piece treated withsodium borate, and one (1) piece of untreated wood. The untreated andsodium borate treated pieces served as controls. During each burn event,flames from two propane torches, one in front and one in back of eachpiece of wood and each slightly offset in opposite direction from thecenter, were directed at the down-side edge of the suspended wood Theburn event was divided into three periods: burn initiation (T₀), burnperiod (T₁₋₂₀), which lasted 20 minutes, and post burn period (T₂₀₋₃₅)when observations were continued 15 minutes after the torches wereturned off. Observations such as amount of flame produced, flame spreador propagation, area of burn, amount of after glowing, percent of woodburned and weight after burning were recorded on data sheets. Each burnevent was also recorded on a video camera.

The method described here for testing the combustible properties oftreated wood is a departure from the standard test method recommended bythe American Standards and Testing Methods (ASTM). Standard method E69-95 (ASTM 1995) describes a method where the combustible material isplaced in an apparatus known as a “fire-tube assembly” and measurementssimilar to that described above are made. The fire-tube apparatus canonly accommodate a small piece of wood, ¾ in×⅜ in×40 in in length, whichis much smaller than the pieces in this study, and can only burn onepiece of wood at a time. I wanted to experiment on pieces of wood thatwere about the same size as wood commonly used by homeowners and Iwanted a side-by-side comparison between treated and non-treated wood.The fire-tube apparatus is also not readily available. The measurementscalled for by this standard method, however, are essentially the same asthose taken during this study.

Candle Tests: The cloth and paper samples and the sodium borate/boricacid treated and untreated controls were each placed in a flame testchamber and tested as described above for the propane flame test withthe exception that the flame was from a 5 in candle. The flame wasdirected at the bottom of the test samples throughout the test period.

In addition water glass treated samples of 2×4 dimension lumber weresubjected to candle flame for 1.5 hours. The nature of burn patternswere in comparison to those of untreated controls.

Thermochemistry of Sodium Silicate Fire Retardant

In order to better characterize the changes occurring during flame testswith sodium silicate impregnated samples, the foam-like residues formedduring the flame tests were subjected x-ray crystallography and by x-rayphoto electron spectrometry. The purpose of the analysis was tochemically identify the composition of the residue from flame tests.This data was then augmented by performing studies of water solubility.

Micro-Layers of Vacuum-Deposited Silicon Oxide Glassy Films

Sodium silicate, while proving to be an effective fire retardant, has anumber of significant problems which limit its use to indoor applicationonly, and prevent its use as a surface coating. The problems inherent tosodium silicate-treated samples were: 1) it was water soluble and thusrain or other moisture could cause the sodium silicate to leach fromtreated products, 2) when sodium silicate was applied directly onto asurface by methods such as painting, coating, and quickly dipping,extensive peeling, cracking and separation from the surface of theproduct occurred.

In the course of about six months it was observed that sodium silicate,when exposed to the air and/or weathered, underwent a physical changefrom a clear, smooth, shiny, material to white, granular, flaky, roughchips. It was also observed that sodium silicate, when protectedcompletely from the air by any of several means, did not undergo thephysical change and remained a clear, smooth, shiny, material.

From these observations, it was concluded that the physical changeobserved for sodium silicate was directly due to exposure to moisture,oxygen and other substances found in the air.

It was hypothesized that after being treated with sodium silicate, if alayer of silicon oxide were deposited over all surfaces, the resultingproduct will retain its flame retardant properties as well as becompletely water proof and completely resistant to deterioration due toexposure to air or the effects of weathering. Because extraordinarilysmall amounts of silicon oxide would be used, the added costs would beexpected to be small.

The present invention thus involves a process of imparting fireretardant properties to a cellulosic material comprising coating acellulosic material comprising coating a cellulosic material with sodiumsilicate by contacting a sodium silicate solution with the material tobe coated, dehydrating the coating, and depositing a coating of asilicon oxide glassy film on the sodium silicate coated material. In oneembodiment, the coating of silicon oxide is a monomolecular layer ofsilicon monoxide.

The following samples were prepared:

-   -   Blocks of wood, 2.5 cm³, presoaked in 40 g/kg sodium silicate,    -   Sections of wood, 2.5 cm×10 cm×0.5 cm, 4 each treated with the        following concentrations: 400 g/kg, 40 g/kg, 4 g/kg, 0.4 g/kg,        and 0.04 g/kg of aqueous sodium silicate, and 4 each controls of        the same concentrations (but not treated with silicon monoxide.

Four of each of the above sample types were held in place with clamps ata 90° angle. Two drops of boiling distilled water was then placed ontoeach sample and allowed to roll across the sample and fall onto amicroscope slide and allowed to evaporate. The samples were thenexamined visually and microscopically for evidence of crystal formation.

Four each of the above sample types were subjected to burn tests, tocompare efficiency of burning with and without the silicon monoxidecoating.

Microscopic Examination of Sodium Silicate and Silicon Oxide TreatedProducts:

To better understand the distribution of sodium silicate throughout thesamples, microscope slides were prepared for selected samples. Theseslides were examined under the microscope and compared to slidesprepared from controls for evidence of sodium silicate distribution andimpregnation of the samples. From these data, information was obtainedon whether soaking procedures resulted in an even distribution of sodiumsilicate throughout the entire sample or whether sodium silicate wasdistributed primarily along the outer edges of the samples.

Example 1 1×4 Pine Propane Flame Tests

FIGS. 3-5 present the results of propane flame tests of sodium silicatetreated 1×4 pine samples.

There is a large difference between the untreated control and the testsamples. With the untreated controls there ranges from about a 40-38%wt. loss to 50% wt. loss, and with the treated samples, it ranges fromabout 15% wt. loss to a 25% wt. loss. As FIG. 3 shows, the boric acidtest samples have a much greater average % weight loss than the treatedsamples. This three dimensional set of bar graphs shows how great thedifference is with each bar graph colorized and labeled.

Propane Flame Test for 1×4 Pine Wood Sample Subjected to a Seven-DaySoak in 100% Sodium Silicate:

Burn initiation (T₀): The propane flame from the nozzle contacted thewood in an area extending 7 cm laterally and reaching up approximately27.5 cm. In the first few seconds the flame color was light blue, andrelatively difficult to see. In the impact area, the wood began glowingin a small circular area approximately 1 inch sq. Immediately afterthis, flame color changed from light blue to yellow orange, presumablydue to the presence of sodium in sodium silicate traveled outward andupward along a curving line from the initial contact point.

Burn period (T₁₋₂₀): During this period, the fire continued to remain inthe pattern described above, with occasional sparks. The flames did notmigrate beyond the flame contact area; however the lower half of theflame contact area was charred. The area at the top edge of the flameflickered orange and below this area the flame was yellow-white incolor.

Post burn period (T₂₀₋₃₅): After the propane flame was extinguished, theflames died down within 5 seconds; however hot, red glowing embers wereobserved in the 1 in square area where the heat and flame reached thehighest temperature. These embers continued to glow and smolder forapproximately 15 minutes. After the embers had cooled a hole,approximately 1 in square was observed at the point of most intenseflame application.

On the sides of the wood, white foam bubbled out from the water glass,traveling up the edge of the face of the wood. This area of white foamprevented the spread of flame and char laterally to the side of thewood. One face side of the sample was 83% covered with char and soot.The other face side was 50% covered with char. The color of the char wasblack, with a thin layer of white foam on the top. There was lesscracking of the char than was found on the control. The small sides ofthe wood remained untouched by either char or fire. The area above theflame reflection took place, had a thin layer of soot in which theunderlying wood was unburned. The foaming of the sides took place muchgreater on the left side of the wood than on the right side. The leftside foamed about 90% more than on the right side of the wood. There wasobserved 0-1% of the small sides burned or charred during the test.

Propane Flame Test for 1×4 Pine Wood Untreated Control Sample, Comparedto 1×4 Soak, 100% Sodium Silicate:

Burn initiation (T₀): The propane flame from the nozzle contacted thewood in a 4 cm diameter, then fire spread up the wood in three lines:one in the center of the sample, and the other two growing up the sides.The flame extended 10 cm from the initial point of contact.

Burn Period (T₁₋₂₀): After two minutes of burning, the flame began todie down to only extending five cm from the initial point of contact.When three minutes and thirty-five seconds had passed, new largernozzles were added to the tank to increase the amount of fire beingapplied to the wood. The flame from the larger propane nozzles extendedto the top of the wood sample and above it, totaling 29 cm at thegreatest height. The flame spread to all sides of the wood, but thesmall right side received the most amount of fire.

Post Burn Period (T₂₀₋₃₅): After the propane tanks were removed from thewood sample, the flames died down within five seconds, leaving two largeholes with the outside edges smoldering. The area where the glowingembers were observed was in a ring of about 2 cm around the large hole.There were two large holes in the sample after the burning was finished.The large hole was 8 cm long and 5½ cm wide. The smaller hole was 2 cmlong and 4 cm wide. Char extended all of the of the wood that had beenabove the initial point of contact. The char is dark black to darkbrown. The area where the char is has many cracks in it, extendingthroughout all of the char area. The small left side of the wood is 15%covered with char; on the right side of the wood, the side is 35%covered with char. The char has a layer of soot over it, and rubs off onskin, clothing, or any other casual contact that may occur.

Propane Test for 1×4 Pine Wood Sample Subjected to a 1-Day Dip in 100%Sodium Silicate:

Burn initiation (T₀): The flame from the nozzle of the propane tankcontacted the wood at the bottom of the sample. The flame began toredden an area of 3 cm², then the flame began to reflect off the wood,with the flame extending 6 cm from the initial point of contact.

Burn Period (T₁₋₂₀): During this period, the flame reflected off thewood sample. The flame itself did not propagate onto the wood sample.The total height of the flame was about 6 cm high and 3 cm wide. Thetops of the flames flickered in the wind. The sound that the wood madewhen it was being burned in a new area was that of a sizzling, andoccasional popping one. A layer of thin char, or soot grew up the woodabove the flame. The layer of ash continued to grow up to the top of thewood. After 10 minutes had passed, the flame died down to a small cinderarea around the initial point of contact.

Post Burn Period (T₂₀₋₃₅): After the flames from the propane tanks wereremoved, the flames on the wood died down in a matter of seconds. Therewere glowing embers around the area where the propane tank had been. Thearea was 5 cm tall and 6 cm wide at the widest point. The wood is 50%covered in char. The color of the ash is from black to dark brown,except for a layer of white sodium silicate byproduct on top of the charand ash in some areas. Along the sides of the wood there is bubblingfrom the sodium silicate. The bubbling is 90% greater on the left sidethan on the right. There is not much charred area on the sides; onlyabout 10% of the sides are burned. There is no burning, charring or sooton the back side of the sample.

Propane Flame Test for 1×4 Pine Wood Untreated Control Sample, Comparedto 1×4 Dip, 100% Sodium Silicate:

Burn initiation (T₀): When the flame is first applied to the testsample, flame begins to climb up the sides of the wood, reaching 20 cmoff the original burn point. The flame began to slowly travel up thesides of the wood, scorching it and spreading soot and char around theburn site.

Burn period (T₁₋₂₀): The flame continues to rise 12 cm up the left sideof the wood sample. The flame adjusts to the middle of the sample,burning up the sample about 13 cm. The flame chars 70% of the wood, asit buns in the center. The top of the flame flickers and wavers in thewind.

Post burn period (T₂₀₋₃₅): The wood sample smolders and burns when thepropane tanks are removed. The area of char on the wood extends from thebottom of the sample, to 6 cm below the top of the wood. The firecharred half of the right side of the wood, and over 75% of the leftside. In the sample, there were large craters in the wood, where theflame had not eaten all the way through the wood. The craters were: 6cm×4 cm, and 5 cm×3 cm. The area where the burning took place had largecracks in it, the area where the cracks were extended all the way thatthe flame did. The top part of the sample that was untouched by flame iscovered in a thin layer of soot and ash. The color of the char is a darkblack to a dark brown.

FIG. 4 shows that the weight loss of the combustion tests were greaterin the samples that had less % water glass impregnated in the testsample. As the % water glass that was in the in the sample increased,the percent weight loss from the combustion test decreased.

FIG. 5 is a second order regression, and it shows the line connectingtwo data points as the regression line. The lines around the regressionline [20], r=0.62. The lines around the regression line [19], 95%Confidence limits, show that 95% of the time, the data will lie withinthose lines.

Example 2 1×4 Pressure Treated Pine Propane Flame Tests

FIGS. 6-7 present the results of propane flame tests of sodium silicatetreated 1×4 pressure treated pine samples.

FIG. 6 shows how great the 5 wt. loss was, of the untreated control andthe boric acid control, and the water glass treated samples. The datashows that in all cases, the water glass samples performed better thanthe boric acid control and better than the untreated control.

Propane Test for 1×4 Pressure Treated Pine Wood Sample Subjected to a1-Day Dip in 100% Sodium Silicate:

Burn initiation (T₀): The flame from the propane tank began to reflectoff the wood sample. The color of the fire was bright orange. The flamereflection extended 13 cm up from the base of the wood. The flame alsobegan to burn up the right side slightly.

Burn Period (T₁₋₂₀): The flames continue to reflect off the sodiumsilicate, only reaching 15 cm high. The flames reach the small leftside, where it is mostly unprotected. The fire spreads quickly up theside without much treatment, while the other sides continue to repel theattacks from the fire. Later on in the test period, the flame rose, andconsumed most of the center of the wood sample.

Post burn period (T₂₀₋₃₅): Most of the center section of the wood andthe right side has been burned away. There is a small chunk of wood thatfell off in burning, but the rest of the missing wood is ash and debris.There was small evidence of the sodium silicate burning, there are 1-2cm² areas where the sodium silicate has bubbled up into foam, but thefoam did no stop the spread of the flame. The part that is missing is 21cm high and 6 cm wide. The color of the intact wood is black, but insome spots the original dark green color is visible.

Propane Flame Test for Untreated Control, 1×4 Pressure Treated Pine,Compared to Dip, 100% Sodium Silicate, Pressure Treated Pine, 1×4:

Burn initiation (T₀): When the flame was applied to the wood, the woodburst into flame, with the fire reached above and beyond the top of thewood. The spread of the fire took place remarkably fast.

Burn period (T₁₋₂₀): The flames on the wood continued to grow andpropagate. The flames spread up all sides of the wood. Slowly, the woodbegan losing its shape, ashes fell and the wood began to deteriorate.

Post burn period (T₂₀₋₃₅): After the propane tanks were removed, thesample continued to smolder and burn until there was nothing left thatit could burn. The cinders kept smoldering for a while, until they diedout as well. The remains of the wood sample weighed only about 3% of theoriginal weight. The remains of the sample could be collected in thebottom of a cup. There were no pieces of wood that could still hold ashape; it had all turned to ash. The color of the ash was a light gray.

Propane Test for 1×4 Pressure Treated Pine Wood Sample Subjected to a7-Day Soak in 100% Sodium Silicate:

Burn initiation (T₀): When the flame first touched the wood sample, theflame reflected off the wood and turned bright orange. The wood sizzledand popped. The flame reflected 9 cm from the first point of contact.

Burn period (T₁₋₂₀): The flame stayed roughly around the same area whereit had been when the test started. The flames did grow some, though. Theflames spread soot and ash around to other parts of the wood. The woodkept its same shape throughout the burning.

Post burn period (T₂₀₋₃₅): The wood sample kept its basic same shapewhen it was taken away from the flame. Its burn area was a small portionon the bottom of the sample. Most of the sample is still good, firmwood. There is evidence of sodium silicate burning on the edge of thecharred parts. The charred parts extended to a few cm short of the topof the wood. Surprisingly, the wood kept its shape.

Propane Flame Test for Untreated Control, 1×4 Pressure Treated Pine,Compared to 7-Day Soak, 100% Sodium Silicate, Pressure Treated Pine,1×4:

Burn initiation (T₀): When flame is first applied to the sample, thefire propagates quickly and starts to spread up the sides of the sample.The fire soon quickens, and begins to spread to other parts of thesample.

Burn period (T₁₋₂₀): The flames on the wood rose, and began to consumethe whole sample. The flames extended above the sample, in the air, andthe sample began to lose shape quickly. The flames continued to eat awayat the burn sample even when the propane tanks were turned off.

Post burn period (T₂₀₋₃₅): After the wood sample was separated from thewood, the sample lost its shape and fell apart into a heap of ash. Theash is all that is left of the sample. The ash is all powder with norecognizable parts in it. The ash is dark gray, to light gray.

FIG. 7 shows the % wt. loss compared to each treated sample. This graph(FIG. 7) is a first order regression [22], r=0.73, bounded by 95%confidence limits [21], which slows that as you lessen the % of waterglass you treat the sample with, and shorten the amount of time thesamples are introduced to the water glass, the % wt. loss increases.

Example 3 2×4 Pine Propane and Candle Flame Tests

Propane Flame Test for 2×4 Spruce Sample Subjected to a 24-Hour Dip in100% Sodium Silicate:

Burn initiation (T₀): The flame from the propane tank began to make anarea of the wood glow. The area that was glowing was 1 inch in diameter.The sample made sizzling and popping noises, and around the burn area,white foam bubbled out of the sodium silicate.

Burn period (T₁₋₂₀): The flame from the propane tank spread about 3 cmaround the initial burn site. No wood propagation occurred in this woodsample. Around and above the burn site, char expanded causing maresodium silicate to bubble up along the outside of the char area. Noflame burned by itself on the wood. Any time that a flame would begin togrow it size, it would die down. Instead of burning, the area around theinitial contact point, the area reddened, and glowed in the heat.

Post burn period (T₂₀₋₃₅): After the propane flame was removed from thetest sample, the wood continued to smolder for a short while. The samplewas only changed from the flame in the bottom 15.5 cm. At the contactpoint of the flame, there was a large crater, 4 cm wide, 3.5 cm long,and 2 cm deep. The walls of the crater are all black, with white foam atground level of the crater. Above the crater, there is cracked char witha thin layer of sodium silicate foam on the top of it. The foamsurrounds all sides of the char. No charring or burning occurred at anyof the small sides of the sample. The back side of the sample iscompletely clear of any burning or charming.

Propane Flame Test for 2×4 Spruce Untreated Control Sample, Compared toDip, 100% Sodium Silicate:

Burn initiation (T₀): When the flame from the propane tank reached thewood, it created an area of charring with a 3 cm diameter from theinitial point of contact. A small flame began to dance on the top of thechar area, but died down with the first gust of wind.

Burn Period (T₁₋₂₀): The char area increased over time, and small flameswould begin to burn, but the flames could not resist the wind. Thepropane flame did not create a fir that propagated on the wood, all itdid was create an area of char, and allow the wood to glow with theheat.

Post burn period (T₂₀₋₃₅): After the propane flame was removed from thewood sample the flames died down quickly. The wood still smoldered, andgave off lots of smoke. The wood was only burned on the front side ofthe sample. There were two craters in the wood, and a large area of charsurrounding them. The charred areas extended from the base of the woodsample to 19 cm above it. The char was a dark black and had many cracksin it.

Example 4 Composite Samples Propane Flame Tests

FIGS. 8-10 present the results of propane flame tests of sodium silicatetreated composite wood samples.

FIG. 8 shows the % wt. loss compared to the sample so plywood. Theuntreated control has a much greater % wt. loss than the boric acid ortreated control. In this test run, the treated samples had a lower % wt.loss than either the boric acid control, or the untreated control.

FIG. 9 shows the % wt. loss compared to the different sample types. Thisgraph shows the large difference between the controls and the testsamples. The test sample had a much lower % weight loss than either theboric acid control or the untreated control.

FIG. 10 shows the % wt. loss compared to the different types of samples.In this test the treated samples had a much lower % wt. loss than eitherthe boric acid or untreated control. The water glass treated sampleshave a much lower flame retardancy than either control.

Example 5 Cloth Samples Candle Flame Tests

FIGS. 11-13 present the results of propane flame tests of sodiumsilicate treated cloth samples.

FIG. 11 shows that the untreated control had almost 100% wt. loss. Inthis test, the boric acid sample had the lowest % weight loss. All ofthe treated samples had a much lower % wt. loss than the control.

In FIG. 12 there is no boric acid sample. This graph shows how dramaticthe results are the control had about a 90% wt. loss, and the samples,at most had about an 11% wt. loss.

Candle Test-Fabric:

Treated sample: Charring in the spot directly in the flame, smokeproduction. Flame does not spread. The felt is getting cracks in theflame area. The area in direct contact with flame is getting bubbles.Smoke occurs only when in the flame. No flame propagation occurred inthe test.

Control sample: The burning started to propagate on the sampleimmediately. The smoke given off was white. The flames reached about 2inches off of the sample. The burning did not occur as fast as wouldhave been forecasted. The sample did not catch fire as much as thecharring just spread.

FIG. 13 shows the 95% confidence limit lines, which shows that as theamount of water glass in the sample increases, the % wt. loss decreases.This shows that the sodium silicate has a major effect on the burncharacteristics of the samples.

Example 6 Paper Samples Candle Flame Tests

FIGS. 14-18 present the results of propane flame tests of sodiumsilicate treated paper samples.

Candle Test—Paper:

Treated sample: The flame darkens the paper, but doe not catch fire. Thepaper sizzles and cracks in response to the fire. The paper itself doesnot catch fire, but does release a lot of smoke. The area of char doesnot go past the initial contact point with the paper. At the points onthe paper that are in direct contact with the flame. It begins toredden, but does not catch fire. The paper thickens as heat is appliedto it. It takes the fire 5 min 33 sec before it can do all of its work.

FIG. 14 shows the % wt. loss compared to the different sample types.This test shows how the sodium silicate treated samples have a much less% wt. loss than the boric acid and untreated controls.

FIG. 15 shows the % wt. loss compared to the different sample types.There is no boric acid control in this test. This test run shows howmuch greater wt. the control loses than the treated samples. this graphis an excellent example of how the sodium silicate effect the burncharacteristics.

Control sample: The flame started up the paper immediately, spreadingquickly up the paper. The fire elevated to ½ of an inch above the paper,the total burn time for the paper to become consumed lasted 17 seconds.The final weight was too small to measure.

FIG. 16 shows % wt loss after burn, compared to the percent water glassafter treatment. The graph shows that as the amount of sodium silicatein the sample increases, the % wt. loss from burn decreases as a secondorder regression r²=0.89 [24], with the 95% confidence limits shown[23]. This can show that sodium silicate has a positive effect on theburn characteristics of paper.

FIG. 17 shows the burn cycle over a 2 hour period. The graph shows thatwhen the flame is first applied, weight loss increases rapidly. Afterabout 20 min the weight loss begins to taper off and continues in analmost straight line.

FIG. 18 is similar to that of FIG. 17. It shows the burn cycle of theflames in a 2 hour period. This graph is a third order regression,r²=0.88, [26] with 95% confidence limits shown [25], which shows thepath of the burn characteristics.

Example 7 1×4 Pine Cubes Termite Tests

To test another benefit of sodium silicate wood treatment, I soakedsmall pieces of wood in sodium silicate and introduced them to termitesto see if the same quality that makes the wood flame resistant wouldalso make the wood termite resistant. I found that the termites did notlike to be around the water glass treated wood, and they did not evenlike to be around the damp paper towels in the test samples, which mayhave contained small amounts of water glass. The termites locatedthemselves in an area as far away from the treated samples as possible,even though the treated wood was their only food source. No woodconsumption occurred.

Example 8 Summary of Results All Samples

FIGS. 19-21 and Tables 2-4 present comparisons of the results obtainedwith all samples tested. For FIGS. 19 and 20, some samples showed animprovement almost infinite because of thorough burning of the untreatedcontrol, these are indicated by [27].

FIG. 19 shows the % improvement of the test sample over the control. Inthe graph, the blue lines represent the boric acid, and the green linesrepresent the sodium silicate treated samples. The graph shows thatsodium silicate is a more effective fire retardant than boricacid/borax.

FIG. 20 shows the % improvement of the boric acid samples over thecontrol. This graph shows that the boric acid is a somewhat effectivefire retardant treatment.

FIG. 21 comprises % wt loss observed in control samples (x-axis), with %improvement over control with waterglass (y-axis). A correlation as afourth order regression (r²-98%) [29] with the 95% confidence limitsshown [28] was found.

TABLE 2 Comparison of Water Glass and Untreated Control Weight LossComparisons Comparisons of Amounts Unburned Percentage # times PercentAverage Average Number of reduction better better Percent amount amounttimes better Percent in weight than than improve- unburned unburned thanimprove- Sample Type loss control control ment (control) (treated)control ment 1 × 4 Pressure treated pine samples Soak-100% WG 59.75 2.87287% 187 8.25 68 8.24 724% Soak-50% WG 41.5 1.825 183%  83% 8.25 49.756.03 503% Dip 100% WG 45.08 1.97 197%  97% 8.25 53.33 6.46 546% Dip-50%WG 24.5 1.36 136%  36% 8.25 32.75 3.97 297% 1 × 4 Pine Samples (Notpressure treated) Soak-100% WG 28.53 2.64 264% 164% 54.1 82.63 1.53  53%Soak-50% WG 27.1 2.44 244% 144% 54.1 81.2 1.5  50% Dip 100% WG 15.631.52 152%  52% 54.1 69.73 1.28  28% Dip 50% WG 19.65 1.75 175%  75% 54.173.75 1.36  36% Composite Products Particle board 61.5 4.61 461% 361%21.5 83 3.86 286% Wafer board 85.45 10.76 1076%  976% 5.8 91.52 15.781477%  Plywood 52.13 4.28 428% 328% 32 84.13 2.63 163% Paper and ClothProducts Paper Spray 46.63 1.87 187%  87% .03 46.63 1554 155333%   PaperSlurry 87.4 34.61 3461%  3361%  10 97.4 9.74 874% Cloth Spray 80.95 5.24524% 424% 0.09 80.95 899 89844%  Cloth Slurry 84.49 14.38 1438%  1338% 9.2 93.69 10.18 918%

TABLE 3 Comparison of Water Glass and Boric Acid Weight Loss ComparisonsComparisons of Amounts Unburned Percentage # times Percent AverageAverage Number of reduction better better Percent amount amount timesbetter Percent in weight than than improve- unburned unburned thanimprove- Sample Type loss control control ment (control) (treated)control ment 1 × 4 Pressure treated pine samples Soak-100% WG 36.85 2.15215% 115%  31.15 68 2.18 118%  Soak-50% WG 18.6 1.37 132% 37% 31.1549.75 1.60 60% Dip 100% WG 22.18 1.47 1475 47% 31.15 53.33 1.71 71%Dip-50% WG 1.6 1.02 102%  2% 31.15 32.75 1.05  5% 1 × 4 Pine Sample (Notpressure treated) Soak-100% WG 17.4 2.00 200% 100%  65.23 82.63 1.26 26%Soak-50% WG 15.97 1.85 185% 85% 65.23 81.2 1.24 24% Dip 100% WG 4.5 1.15115% 15% 65.23 69.73 1.07  7% Dip 50% WG 8.52 1.32 132% 32% 65.23 73.751.13 13% Composite Products Particle board 38.4 3.26 326% 226%  44.6 831.86 86% Wafer board 78.35 9.95 995% 895%  12.9 91.52 7.09 609%  Plywood10.13 1.64 164% 64% 74 84.13 1.14 14% Paper and Cloth Products PaperSpray 34.13 1.64 164% 64% 12.5 46.63 3.73 273%  Paper Slurry — — — — — —— — Cloth Spray −7.95 0.58  58% −42%  88.9 80.95 0.91 −9% Cloth Slurry —— — — — — — —

TABLE 4 Comparison of Boric Acid and Untreated Control Weight LossComparisons Comparisons of Amounts Unburned Percentage # times PercentAverage Average Number of reduction better better Percent amount amounttimes better Percent in weight than than improve- unburned unburned thanimprove- Sample Type loss control control ment (control) (treated)control ment 1 × 4 Pressure treated pine samples Soak-100% WG 22.9 1.33133% 33% 8.25 31.15 377 277% Soak-50% WG 22.9 1.33 133% 33% 8.25 31.15377 277% Dip 100% WG 22.9 1.33 133% 33% 8.25 31.15 377 277% Dip-50% WG22.9 1.33 133% 33% 8.25 31.15 377 277% 1 × 4 Pine Samples (Not pressuretreated) Soak- 100% WG 11.13 1.32 132% 32% 54.1 65.23 1.2  20% Soak-50%WG 11.13 1.32 132% 32% 54.1 65.23 1.2  20% Dip 100% WG 11.13 1.32 132%32% 54.1 65.23 1.2  20% Dip 50% WG 11.13 1.32 132% 32% 54.1 65.23 1.2 20% Composite Products Particle board 23.1 1.34 134% 34% 21.5 44.6 2.1110% Wafer board 7.1 1.08 108%  8% 5.8 12.9 2.22 122% Plywood 42 2.61261% 161%  32 74 2.31 131% Paper and Cloth Products Paper Spray 12.51.14 114% 145%  0.03 12.5 416.66 41566%  Paper Slurry — — — — — — — —Cloth Spray 88.9 9.00 900% 800%  0.09 88.9 987.77 98677%  Cloth Slurry —— — — — — — —

The percent weight loss for regular 1×4s and 2×4s was lower than forpressure treated pine. This was probably due to the fact that theresults were obtained under different burn conditions. These tests wereperformed outdoors where it was windy and very cold, also only one torchwas used with a very small flame. If I were to repeat the test using theconditions for the pressure treated pine samples, I would expect theresults to be similar to those for pressure treated pine samples.

Example 9 Microscopic Evaluation

The goal for the microscopic examinations was to determine thedistribution pattern of sodium silicate throughout the materials testedin order to determine whether sodium silicate distribution varies as theapplication technique and concentration is varied, and to determinewhether the fire retardant properties observed for sodium silicate areexclusively due to the protective effect of a surface coating, orwhether other mechanisms may also apply, to determine whether sodiumsilicate was able penetrate into pores of the wood or also able to enterand alter cellular structures.

Cross sections of yellow pine samples treated with 300 g/kg sodiumsilicate solution were examined at 30× using a Nikon dissectingstereoscope. FIG. 22 presents the cross section view of a yellow pinesample treated with 300 g/kg sodium silicate solution. In FIG. 22 sodiumsilicate can be clearly seen as a layer at the surface that extends intothe interior in a crevice in the wood, and also can be seen to havespread into the cellular structures in the interior of the sample, notethe white, crystal like areas throughout the sample.

Example 10 Thermochemistry

In addition to the studies examining the flame retardant properties ofsodium silicate treated samples in flame tests described above, sodiumsilicate foam-like material form during the above reported flame testswas investigated. Two areas of investigation were undertaken: 1)chemical composition of the sample formed during flame tests, and 2)solubility of the material formed as a function of temperature of flameor heat.

To know for certain that the material formed in flame tests was not acrystalline substance, the sample was examined using x-raycrystallography. FIG. 23 presents these results which definitely showthat the material is not crystalline in structure. The hardened,foam-like material was then examined using. This method was chosenbecause it would be definitely possible to determine the elementalcomposition of the material and because it is sometime possible todetermine the structure of large molecules using this method. Theresults of x-ray photoelectron spectrometry are presented in FIG. 24.The data show that the material is composed of sodium, oxygen, silicon,when a harden layer of sodium silicate that had not been subjected toheat was analyzed, the results were virtually identical to those shownin FIG. 24, in peak height and intensity. It was not possible tocharacterize the heat treated sample further, apparently due to the verylarge size of the molecules. Attempts to further understand thecharacteristics of the heat treated sodium silicate material, thenemphasized water solubility studies.

Water solubility of sodium silicate is well documented in the publishedliterature (Hawley 1971). This investigator has observed that sodiumsilicate dissolves more slowly after it has hardened into a glassylayer, but does eventually dissolve in agreement with the literature.Sodium silicate was found to be especially soluble in hot or boilingwater. At 100° C. a hardened sample of sodium silicate dissolvedcompletely in less than 20 seconds. In samples treated with 400 μgsodium silicate by soaking for 7 days and then drying and storing, thatwere placed in distilled water at 100° C., all sodium silicate on thesurface and in the interior of the samples was dissolved within 60seconds.

To further study the solubility of sodium silicate treated wood;popsicle sticks soaked with 400 g/kg of sodium silicate were exposed toheat, for five minutes. The sodium silicate treated samples were heatedto 650° C., 260° C., 205° C., and 150° C. The heat treated samples wereplaced in boiling water, and disappearance of sample was used as anindication of solubility. FIG. 25 shows the effect of temperature onsolubility of sodium silicate. The dashed line [30] reports the hoursrequired to dissolve sodium silicate vs. the heating temperature of thesodium silicate heat-treated samples. The solid line [31] shows thepercentage of sodium silicate sample dissolving vs. the heatingtemperature of the sodium silicate heat-treated samples. FIG. 25 showsthat as the temperature increased, the time to dissolve increased aswell. The graph also showed that as temperature decreased, the percentdissolution (read on the right scale) increased.

This data definitely shows that although the substances before and afterburning are composed of the same elements in similar proportions, thewater solubility of the substances is very different. A possibleexplanation for this obvious difference in properties is that as aresult of the application of heat, the sodium silicate undergoesdehydration (loss of water) and a process of polymerization that formsincreasingly larger moieties of (SiO₄)_(n) ⁻¹ while still maintaining anoverall charge of −1 that forms an association with the free sodium. Asthe material polymerizes the resultant material increases in size to thepoint that it is no longer able to dissolve in water, thus becominginsoluble. At lower temperatures, the process would occur to variousdegrees based on the temperatures and the duration of exposure, thusproviding a possible explanation for the partial solubilities observedin FIG. 25.

Example 11 Silicon Monoxide

A major problem adversely affecting the widespread commercialsuitability of sodium silicate as fire retardant, is the watersolubility, and the surface deterioration resulting from exposure to airand moisture, as was described above. This adverse property excludesmany possible applications for sodium silicate treated materials,including the possible external application for materials such asshingles, or decking material.

A possible solution for this problem would be to apply the technologyfor vapor deposition of silicon monoxide to sodium silicate treatedsamples. Silicon monoxide is used currently for computer microchipcoating and is used to a limited extent as a treatment for plastic wrapto provide a moisture proof packaging material.

The results obtained from studies of sodium silicate treatment andsodium silicate/silicon monoxide treatment of various cellulosic samplesare presented below. Ten sample types, treated with sodium silicate byfive different methods, were tested. Two additional treatment methods,application of a micron thin layer of silicon monoxide by vapordeposition, and temperature occurring were then tested with sodiumsilicate samples, were then evaluated, with the objective of eliminatingthe high water solubility observed in sodium silicate treated samples.

In the present study, vapor deposition of silicon monoxide wasaccomplished using bench scale laboratory equipment requiring much morestringent conditions than that required in a commercial application.However under laboratory conditions it was possible to demonstrate thepossibility of coating wood with silicon monoxide, a feat not previouslyattempted. The process of vapor deposition involved placing siliconmonoxide granules in a tungsten basket filament, and creating a strongvacuum of 1.2×10⁻⁵. The filament was then heated to a bright white heat,and the silicon monoxide was vaporized and dispersed throughout thechamber. Once the vacuum levels were reached and the filament reachedthe appropriate temperature, vapor deposition was accomplished inapproximately one minute. By this method a layer of silicon monoxide thethickness of a few molecules was applied to the surface of sodiumsilicate treated wood samples.

When the samples were removed from the vaporization chamber, they wereexamined under a stereoscope, and no visual differences between sodiumsilicate treated wood samples, and silicon monoxide coated sodiumsilicate treated wood samples could be determined.

After the visual examinations, a water test was performed to test thehypothesis. A drop of 90° C. distilled water was placed on the surfaceof a sodium silicate and silicon monoxide treated sample, and on thesurface of a sodium silicate treated control sample. The water dropleton the control sample was instantly absorbed by the wood, and began tosoak through the material. When the water droplet was placed on thesodium silicate and silicon monoxide treated sample, the droplet balledup on the surface of the wood and remained there. No amount of the waterdroplet entered the wood. When the water droplet was examinedmicroscopically, tiny air bubbles were observed on the surface of thesample, beneath the water droplet. These droplets resembled the airdroplets found at the surface of a beaker when water is heating to theboiling point. The silicon oxide apparently prevented the water frompenetrating to the interior portions of the wood sample.

This simple experiment indicated that the properties of silicon monoxide(glass) had been extended to the sodium silicate treated wood samples,including providing a moisture barrier and the associated protectionfrom exposure to air. By this method, the disadvantages of sodiumsilicate alone may be overcome.

FIG. 26 presents the results of burn tests of samples treated by vapordeposition with silicon monoxide following sodium silicate treatment.Comparisons of percent of sample remaining unburned during the 6-10 minburn trials are presented for wood samples treated with 400 g/kg, sodiumsilicate solution, followed by application of vapor deposition coatingof silicon monoxide [32], wood samples treated with 300 g/kg sodiumsilicate solution, followed by application of vapor deposition coatingof silicon monoxide [33], and untreated wood control samples to which avapor deposition coating of silicon monoxide [34], was applied.

FIG. 27 presents the weight loss profiles of sodium silicate treatedcontrols. Comparisons of percent of sample remaining unburned during,the 5 min burn trials are presented for wood samples treated with 400g/kg sodium silicate solution [35], wood samples treated with 300 g/kgsodium silicate solution [36], and untreated wood control samples [37],was applied.

Although the intended purpose was simply to demonstrate that the siliconmonoxide treated samples were at least equivalent in fire retardantproperties to the samples treated with sodium silicate alone, FIG. 26,when compared to the control (FIG. 27) showed a surprising increase infire retardant properties. The data indicate that the total final weightloss was low (85%) and that this weight loss did not begin until wellafter the control had been completely consumed in the flame. Thistechnique therefore not only is capable of eliminating the problems ofleaching and surface deterioration associated with sodium silicate, butalso is capable of providing enhanced fire retardant properties.

In a preferred form of the invention I have coated samples with a onemicron thick silicon oxide containing coating.

The vapor deposition of silicon monoxide resulted in a molecular layerof silicon monoxide imparted on the surface of the sample, although thesample remained visually unchanged, due to the thinness of the layer ofsilicon monoxide.

To further test the integrity of the silicon monoxide moisture barrier,another test was performed. The test included placing water droplets onthe surface of treated and untreated wood samples for 10 seconds, andthen transferring the droplets to microscope slides for evaporation andexamination of the resulting dried material. The results of this testshowed that sodium silicate related crystals similar to those observedearlier in pulverized wood/sodium silicate samples were found in thedried droplets of wood samples treated only with sodium silicate. Thewater droplet from the sodium silicate treated and silicon monoxidetreated sample showed no evidence of sodium silicate crystallization.The results from the tests support the use of silicon monoxidemonolayers as an effective moisture barrier for sodium silicate treatedwood samples.

This finding is also applicable to other substances in addition tosodium silicate, for example the many other inorganic fire retardantchemicals, all of which are water soluble. It is the water solubility ofsome of the most effective fire retardants that have prevented theirutilization on a wide scale.

This presents a possible solution to the ages-old problem of providing afire retardant that is also moisture resistant.

The data show that water glass treatment may be effective in preventingflame propagation throughout wood samples. Even though the wood willburn in areas in direct contact with hot flame, the flames will notspread. This will help to keep small fires from spreading into largeones.

In all samples tested, including standard building materials: 1×4s,2×4s, and pressure treated 1×4s, treatment with water glass was found tocause a reduction in flame propagation and in total amount of woodcombustion.

For all samples flame resistance tended to increase as the concentrationof water glass increased.

The greatest difference between the treated samples and the control wasfound with samples that were highly flammable for example paper andcloth.

In addition, since most fires start with flammable materials inside abuilding such as with paper and drapery, the findings that flammabilitycan be reduced by up to 90% with the use of water glass, suggests thatthis substance may have potential for fire prevention in paper and clothproducts.

In general, the more easily combustible the substance studied, thegreater was the fire retardant effect of sodium silicate.

It was found that it was surprisingly difficult to get solid wood toburn, this was only accomplished when full force flames from the largenozzles of two blow torches were simultaneously directed onto 1×4untreated pine samples. All of the samples burned more readily includingpressure treated pine samples which burned thoroughly and easily. Themost easily burned wood-based sample was wafer board which proved to behighly combustible.

Of all wood-based samples wafer board frame resistance was the mostimproved after treatment with water glass.

Sodium silicate, water glass, does appear to be an effective fireretardant chemical. This represents a new use for this chemical.

As can be concluded, wood products commonly used in constructionincluding dimension lumber, plywood, particle board, and wafer board,and samples of paper and fabric were treated with sodium silicate(Na₂O.SiO₂, commonly known as water glass) in concentrations rangingfrom 400 g/kg to 0.04 g/kg and with Na₂O.SiO₂/vapor deposited siliconmonoxide oxide (SiO₂) laminates to test the hypothesis that treatmentwith sodium silicate solutions would cause otherwise flammable materialsto exhibit fire retardant properties, and to determine the effectivenessof these materials in terms of fire resistance, durability, duration ofeffectiveness, and moisture resistance.

For sodium silicate as a sole treatment, flame retardance was found toincrease as concentration of sodium silicate in solution increased. Atthe 200 g/kg concentration and above, no flame spread was observed andthe improvement in fire resistance (as measured by reduction in totalweight loss) ranged from 40% for 1×4 dimension lumber and furniture to99% for plywood, particle board and shingles.

Fire retardance was found to increase as sodium silicate increased. Insamples treated by soaking in a 0.04 g/kg sodium silicate solution, nodifference was observed between treated and untreated samples. At sodiumsilicate application concentrations ranging from 0.4 g/kg to 4 g/kg,flame retardance was found to increase as concentration of sodiumsilicate in solution increased, at concentrations of 40 g/kg and abovefire resistance was greatest and was essentially unchanged. At the10-400 g/kg concentrations, no flame spread was observed and theimprovement in fire resistance (as measured by reduction in total weightloss) ranged from 75% for 1×4 dimension lumber and furniture to 99% forplywood, particle board and shingles. In flame tests with sodiumsilicate treated samples, sodium silicate was found to form a hardfoam-like material that created a physical barrier as well as chemicalbarrier against flame spread.

Sodium silicate was found to be highly water soluble before flame testsand water insoluble after flame tests. A possible explanation for thisdifference is that as a result of the application of heat, the sodiumsilicate undergoes dehydration (loss of water) and a process ofpolymerization that forms increasingly larger moieties of (SiO₄)_(n) ⁻¹while still maintaining an overall charge of −1 that forms anassociation with the free sodium. As the material polymerizes theresultant material increases in size to the point that it is no longerable to dissolve in water, thus becoming insoluble and increasinglyglass-like. At lower temperatures, the process apparently occurred tovarious degrees based on the temperatures and the duration of exposure.

It was found that in samples soaked in sodium silicate and then dried,that a layer of sodium silicate formed on all surfaces and sodiumsilicate was found throughout the interior of the sample when examinedmicroscopically. When sodium silicate and wood fragments were mixed, theresult was crystal formations not observed with either sodium silicatealone or aqueous wood slurries alone. Sodium silicate impregnatedsamples were found to be more resistant to compression and to weigh lessthan untreated samples. Sodium silicate treated samples were found to becapable of performing woodworking applications such as hammering,cutting, and nailing. In terms of duration of effectiveness, in testsconducted over a one year period, it was found that in samples that hadbeen soaked in sodium silicate solutions for several hours to severaldays, the coating were still intact although they were white andsomewhat chalky. In samples that were quickly dipped in sodium silicatewith the result that a relatively thick layer of sodium silicate wasformed on the surface, the coatings remained completely intact butbecame deeply cracked and a thin layer of white granular material wasobserved on the outer surfaces in the areas directly in contact withair. In samples in which a thin layer of sodium silicate was appliedwith a painting technique, such as used for painting walls and infurniture finishing, over a period of a few months all of the sodiumsilicate layer had cracked and sloughed off. Samples of sodium silicateapplied to glass slides and examined microscopically showed evidence ofthe beginning of cracking with a one hour time period; there were largerand deeper cracks in thicker samples with higher concentrations, andsmaller and more numerous cracks in thinner samples with lowerconcentrations. In summary cracking and peeling, and surface granulationupon exposure to air and moisture are problems associated with the useof sodium silicate.

In terms of moisture resistance, sodium silicate soaked samples wereexposed to effects of weathering for a one year period. It was foundthat there was evidence of leaching of sodium silicate from the wood,with approximately fifty percent of the sodium silicate removed afterone year. Sodium silicate wafers dissolved in boiling water within 30-60seconds. Thus surface layers of sodium silicate were shown to be veryvulnerable to moisture. In samples in which sodium silicate wasinitially applied in small drops, after one year of weathering, thesodium silicate curled up and away from the wood in small white flakes.In samples soaked in sodium silicate, no visible flaking was observedafter a one-year period. Samples soaked at concentrations of 300 g/kgand below no there was visible evidence of the presence of sodiumsilicate on the surface at any time.

Samples treated with sodium silicate by soaking in 200-300 g/kgconcentrations followed by drying were found to be highly flameretardant in interior applications where contact with water would beprevented. Samples soaked 1-7 days in 300 g/kg sodium silicate solutionsand below were found to experience no observable deterioration and noloss in fire retardant capability after a one year time period, althoughadverse effects of water solubility, chipping and peeling, and surfacegranulation were observed for other concentrations and applicationmethods. No adverse effects on conventional uses of wood such as forhammering, nailing, and drilling were observed for sodium silicatetreated samples.

Two additional approaches were utilized to study the problems ofmoisture resistance and chipping and flaking. One-year-old samplescontaining sodium silicate foam formed during burn tests were placed ina container of boiling water. It was observed that the foam samplesfloated in the water and did not dissolve during a 5 minute boiling testand subsequent soaking for over 24 hours. These samples showed nochanges in the foam over a one-year period.

Sodium silicate treated samples were dried and then a molecular layer ofsilicon monoxide was applied to all surfaces by vapor deposition. Thesamples were tested for moisture resistance by applying a stream ofboiling water to the surface of the samples, and the water was examinedmicroscopically for evidence of sodium silicate crystals as the waterevaporated. No evidence of sodium silicate presence was detected,indicating the desired moisture resistance was achieved.

The application of a micro layer of silicon monoxide glassy films to thesurface of a sodium silicate treated sample provided a product that wasstrong, fire retardant, and moisture resistant, and therefore effectivefor internal and external uses. Sodium silicate, was found to be aneffective fire retardant material, and when combined with the siliconmonoxide was found to solve the problems of lack of moisture resistanceand leaching.

In addition, cellulosic materials including dimension lumber, plywood,particle board, wafer board, paper, and fabric were treated with sodiumsilicate (Na2O.SiO2) in concentrations ranging from 400-0.04 gNa2O.SiO2/kg water and the surfaces of selected samples were furthertreated with silicon monoxide (SiO), applied in a molecular layer byvapor deposition. Tests were conducted to determine the effectiveness ofthese materials in terms of fire resistance, durability, duration ofeffectiveness, and moisture resistance. For sodium silicate as a soletreatment, flame retardance was found to increase as concentration ofsodium silicate in solution increased. At the 200 g/kg concentration andabove, no flame spread was observed and the improvement in fireresistance (as measured by reduction in total weight loss) ranged from40% for 1×4 dimension lumber and furniture to 99% for plywood, particleboard and shingles.

Samples treated with sodium silicate by soaking in 200-300 g/kgconcentrations followed by drying were found to be highly flameretardant in interior applications where contact with water would beprevented. Samples soaked 1-7 days in 300 g/kg sodium silicate solutionsand below were found to experience no observable deterioration and noloss in fire retardant capability after a one year time period, althoughadverse effects of water solubility, chipping and peeling, and surfacegranulation were observed for other concentrations and applicationmethods. No adverse effects on conventional uses of wood such as forhammering, nailing, and drilling were observed for sodium silicatetreated samples.

To overcome the disadvantages of sodium silicate, sodium silicatetreated samples were further treated by the deposition of a molecularcoating of silicon monoxide by vapor deposition. Samples treated by thistechnique were found to be completely moisture resistant. The combinedapplication of sodium silicate and silicon monoxide was found to providea fire retardant product that is moisture resistant and decompositionresistant, and therefore effective for internal and external uses.Sodium silicate coated with a thin layer of silicon monoxide does appearto provide an effective fire retardant material.

1. A method of bonding fibers of cellulosic material into a consolidatedmass, said method comprising: adding an aqueous binder solutionconsisting essentially of sodium silicate to a mass of separatecellulosic fibers, forming said separate fibers into a coherent mass,and bonding said mass of fibers by drying said aqueous solution, andthereafter converting said sodium silicate into a water insoluble. 2.The method of claim 1 wherein said coherent mass forms paper.
 3. Themethod of claim 1, wherein said coherent mass is a felt.
 4. A bondedcellulosic fiber product made by the process of claim 1.